Image and Video Processing
AI-Based Detection of Temporal Changes in MR-Linac Images Acquired During Routine Prostate Radiotherapy
Seungbin Park, Peilin Wang, Ryan Pennell et al. (+6 more)
Purpose: To investigate whether an AI-based method can detect subtle inter-fraction changes in MR-Linac images acquired during radiotherapy and explore the broader potential of MRLinac imaging. Methods: This retrospective study included longitudinal 0.35T MR-Linac images from 761 patients. To identify temporal changes, we employed a deep learning model using temporal ordering via pairwise comparison, previously shown effective for longitudinal imaging studies. The model was trained using first-to-last fraction pairs (F1-FL) and all pairs (All-pairs). Performance was assessed using quantitative metrics (accuracy and AUC) and compared against a radiologist's performance. Qualitative evaluation was performed using saliency maps, which identify anatomical regions associated with temporal imaging changes. Results: The F1-FL model demonstrated high performance (AUC=0.99, accuracy=0.95) and outperformed the radiologist in temporal ordering task. The All-pairs model also showed high performance (AUC=0.97, accuracy=0.91). Regions contributing to predictions included the prostate, bladder, and pubic symphysis. The performance was correlated to fractional intervals and was reduced for non-radiation-exposed timepoints (Sim and F1), suggesting that observed changes may reflect both temporal variation and radiation exposure. Conclusion: MR-Linac imaging appears capable of capturing subtle changes during prostate radiotherapy that can be detected by AI models, even over approximately two-day intervals. The model's high performance, together with quantitative and qualitative analyses, supports a potential role for MR-Linac in clinical applications beyond image guidance.
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All authors Seungbin Park, Peilin Wang, Ryan Pennell, Emily S. Weg, Himanshu Nagar, Timothy McClure, Mert R. Sabuncu, Daniel Margolis, Heejong Kim
Systems and Control
Multi-Sensor Scheduling for Remote State Estimation over Wireless MIMO Fading Channels with Semantic Over-the-Air Aggregation
Minjie Tang, Photios A. Stavrou and Marios Kountouris
In this work, we study multi-sensor scheduling for remote state estimation over wireless multiple-input multiple-output (
MIMO) fading channels using a novel semantic over-the-air (SemOTA) aggregation approach. We first revisit Kalman filtering with conventional over-the-air (OTA) aggregation and highlight its transmit power limitations. To balance power efficiency and estimation performance, we formulate the scheduling task as a finite-horizon dynamic programming (DP) problem. By analyzing the structure of the optimal Q-function, we show that the resulting scheduling policy exhibits a semantic structure that adapts online to the estimation error covariance and channel variations. To obtain a practical solution, we derive a tractable upper bound on the Q-function via a positive semidefinite (PSD) cone decomposition, which enables an efficient approximate scheduling policy and a low-complexity remote estimation
algorithm. Numerical results confirm that the proposed scheme outperforms existing methods in both estimation accuracy and power efficiency.
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Image and Video Processing
Smart Diagnosis and Early Intervention in PCOS: A Deep Learning Approach to Women's Reproductive Health
Shayan Abrar, Samura Rahman, Ishrat Jahan Momo et al. (+4 more)
Polycystic Ovary Syndrome (PCOS) is a widespread disorder in women of reproductive age, characterized by a hormonal imbalance, irregular periods, and multiple ovarian cysts. Infertility, metabolic syndrome, and cardiovascular risks are long-term complications that make early detection essential. In this paper, we design a powerful framework based on transfer learning utilizing DenseNet201 and ResNet50 for classifying ovarian ultrasound images. The model was trained on an online
dataset containing 3856 ultrasound images of cyst-infected and non-infected patients. Each ultrasound frame was resized to 224x224 pixels and encoded with precise pathological indicators. The MixUp and CutMix augmentation strategies were used to improve generalization, yielding a peak validation accuracy of 99.80% by Densenet201 and a validation loss of 0.617 with alpha values of 0.25 and 0.4, respectively. We evaluated the model's interpretability using leading Explainable AI (XAI) approaches such as SHAP, Grad-CAM, and LIME,
reasoning with and presenting explicit visual reasons for the model's behaviors, therefore increasing the model's transparency. This study proposes an automated system for medical picture diagnosis that may be used effectively and confidently in clinical practice.
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All authors Shayan Abrar, Samura Rahman, Ishrat Jahan Momo, Mahjabin Tasnim Samiha, B. M. Shahria Alam, Mohammad Tahmid Noor, Nishat Tasnim Niloy
Image and Video Processing · Cross-listed from cs.LG
Comparing Euclidean and Hyperbolic K-Means for Generalized Category Discovery
Mohamad Dalal, Thomas B. Moeslund and Joakim Bruslund Haurum
Hyperbolic representation learning has been widely used to extract implicit hierarchies within data, and recently it has found its way to the open-world classification task of Generalized Category Discovery (GCD). However, prior
hyperbolic GCD methods only use
hyperbolic geometry for representation learning and transform back to Euclidean geometry when clustering. We hypothesize this is suboptimal. Therefore, we present
Hyperbolic Clustered GCD (HC-GCD), which learns
embeddings in the Lorentz Hyperboloid model of
hyperbolic geometry, and clusters these
embeddings directly in
hyperbolic space using a
hyperbolic K-Means
algorithm. We test our model on the Semantic Shift
Benchmark datasets, and demonstrate that HC-GCD is on par with the previous state-of-the-art
hyperbolic GCD method. Furthermore, we show that using
hyperbolic K-Means leads to better accuracy than Euclidean K-Means. We carry out ablation studies showing that clipping the norm of the Euclidean
embeddings leads to decreased accuracy in clustering unseen classes, and increased accuracy for seen classes, while the overall accuracy is
dataset dependent. We also show that using
hyperbolic K-Means leads to more consistent clusters when varying the label granularity.
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Image and Video Processing · Cross-listed from physics.optics
ConvRML: high-quality lensless imaging with random multi-focal lenslets
Leyla A. Kabuli, Clara S. Hung, Vasilisa Ponomarenko et al. (+2 more)
Mask-based lensless imagers use simple optics and computational reconstruction to design compact form factor cameras with compressive imaging ability. However, these imagers generally suffer from poor reconstruction quality. Here, we describe several advances in both hardware and software that result in improved lensless imaging quality. First, we use a precision-manufactured random multi-focal lenslet (RML) phase mask to produce improved measurements with reduced multiplexing. Next, we implement a ConvNeXt-based reconstruction architecture, which provides up to 4.6 dB improvement in peak signal-to-noise ratio over state-of-the-art
attention-based architectures. Finally, we establish a parallel imaging setup that simultaneously images a scene with RML, diffuser, and lens systems, with which we collect
datasets with 100,000 measurements for each system, to be used for reconstruction model training and evaluation. Using this standardized system, we quantify the improved measurement quality of the RML compared to a diffuser using the modulation transfer function and mutual information. Our ConvRML system benefits from both the optical and the computational developments presented in this work, and our contributions establish resources to support the continued development of high-quality, compact, and compressive lensless imagers.
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All authors Leyla A. Kabuli, Clara S. Hung, Vasilisa Ponomarenko, Eric Markley, Laura Waller
Systems and Control · Cross-listed from quant-ph
Review of Superconducting Qubit Devices and Their Large-Scale Integration
Hiu Yung Wong
The superconducting
qubit quantum computer is one of the most promising
quantum computing architectures for large-scale integration due to its maturity and close proximity to the well-established
semiconductor manufacturing infrastructure. From an education perspective, it also bridges classical microwave electronics and
quantum electrodynamics. In this paper, we will review the basics of
quantum computers, superconductivity, and Josephson junctions. We then introduce important technologies and concepts related to DiVincenzo's criteria, which are the necessary conditions for the superconducting
qubits to work as a useful
quantum computer. Firstly, we will discuss various types of superconducting
qubits formed with Josephson junctions, from which we will understand the trade-off across multiple design parameters, including their noise immunity. Secondly, we will discuss different schemes to achieve
entanglement gate operations, which are a major bottleneck in achieving more efficient fault-tolerant
quantum computing. Thirdly, we will review readout engineering, including the implementations of the Purcell filters and
quantum-limited amplifiers. Finally, we will discuss the nature and review the studies of two-level system defects, which are currently the limiting factor of
qubit coherence time. DiVincenzo's criteria are only the necessary conditions for a technology to be eligible for
quantum computing. To have a useful
quantum computer, large-scale integration is required. We will review proposals and developments for the large-scale integration of superconducting
qubit devices. By comparing with the application of electronic design automation (EDA) in
semiconductors, we will also review the use of EDA in superconducting
qubit quantum computer design, which is necessary for its large-scale integration.
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Signal Processing
Safe-NEureka: a Hybrid Modular Redundant DNN Accelerator for On-board Satellite AI Processing
Riccardo Tedeschi, Luigi Ghionda, Alessandro Nadalini et al. (+5 more)
Low Earth Orbit (LEO) constellations are revolutionizing the space sector, with on-board Artificial Intelligence (AI) becoming pivotal for next-generation satellites. AI acceleration is essential for safety-critical functions such as autonomous Guidance,
Navigation, and Control (GNC), where errors cannot be tolerated, and performance-critical processing of high-bandwidth sensor data, where occasional errors are tolerable. Consequently, AI accelerators for satellites must combine robust protection against radiation-induced faults with high throughput. This paper presents Safe-NEureka, a Hybrid Modular Redundant Deep Neural Network (DNN) accelerator for heterogeneous RISC-V systems. It operates in two modes: a redundancy mode utilizing Dual Modular Redundancy (DMR) with hardware-based recovery, and a performance mode repurposing redundant datapaths to maximize parallel throughput. Furthermore, its
memory interface is protected by Error Correction Codes (ECCs), and the controller by Triple Modular Redundancy (TMR). Implementation in GlobalFoundries 12nm technology shows a 96 reduction in faulty executions in redundancy mode, with a manageable 15 area overhead. In performance mode, the architecture achieves near-baseline speeds on 3x3 dense convolutions with a 5 throughput and 11 efficiency reduction, compared to 48 and 53 in redundancy mode. This flexibility ensures high overheads are limited to critical tasks, establishing Safe-NEureka as a versatile solution for space applications.
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All authors Riccardo Tedeschi, Luigi Ghionda, Alessandro Nadalini, Yvan Tortorella, Arpan Suravi Prasad, Luca Benini, Davide Rossi, Francesco Conti
Systems and Control
SQP-Based Cable-Tension Allocation for Multi-Drone Load Transport
Lamberto Vazquez-Soqui, Fatima Oliva-Palomo, Diego Mercado-Ravell et al. (+1 more)
Multi-
Agent Aerial Load Transport Systems (MAATS) offer greater payload capacity and fault tolerance than single-drone solutions. However, they have an underdetermined tension allocation problem that leads to uneven energy distribution, cable slack, or collisions between drones and cables. This paper presents a real-time optimization layer that improves a hierarchical load-position-attitude controller by incorporating a Sequential Quadratic Programming (SQP)
algorithm. The SQP formulation minimizes the sum of squared cable tensions while imposing a cable-
alignment penalty that discourages small inter-cable angles, thereby preventing tether convergence without altering the reference trajectory. We tested the method under nominal conditions by running numerical simulations of four quadrotors. Computational experiments based on numerical simulations demonstrate that the SQP routine runs in a few milliseconds on standard hardware, indicating feasibility for real-time use. A sensitivity analysis confirms that the gain of the cable-
alignment penalty can be tuned online, enabling a controllable trade-off between safety margin and energy consumption with no measurable degradation of tracking performance in simulation. This framework provides a scalable path to safe and energy-balanced cooperative load transport in practical deployments.
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All authors Lamberto Vazquez-Soqui, Fatima Oliva-Palomo, Diego Mercado-Ravell, Pedro Castillo
Audio and Speech Processing
LALM-as-a-Judge: Benchmarking Large Audio-Language Models for Safety Evaluation in Multi-Turn Spoken Dialogues
Amir Ivry and Shinji Watanabe
Evaluation of socially unsafe content in spoken dialogues remains text-centric, missing prosody and transcription failures. We present LALM-as-a-Judge, which includes an open
benchmark of 24,000 multi-turn spoken dialogues with one localized unsafe turn, generated out of 8 socially unsafe categories and 5 severity levels. We evaluate 6 large audio-
language models (LALMs) as judges, open and closed-source, in text-only, audio-only, and
multimodal setups by their sensitivity, severity-order specificity, and turn-position bias for socially harmful content in the dialogue. Results show that audio contributes non-lexical evidence beyond transcript semantics and that
multimodal gains are not universal but can be text-anchored, balanced, conservative, and interfering, which we link to the audio pathway bottlenecks and fusion limits. We position the
benchmark as diagnostic and derive practitioner guidance for model, modality, and
prompts choices.
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Signal Processing · Cross-listed from cs.LG
Maximum-Volume Nonnegative Matrix Factorization
Olivier Vu Thanh and Nicolas Gillis
Nonnegative
matrix factorization (NMF) is a popular data
embedding technique. Given a nonnegative data
matrix $X$, it aims at finding two lower dimensional
matrices, $W$ and $H$, such that $X\approx WH$, where the factors $W$ and $H$ are constrained to be element-wise nonnegative. The factor $W$ serves as a basis for the columns of $X$. In order to obtain more interpretable and unique solutions, minimum-volume NMF (MinVol NMF) minimizes the volume of $W$. In this paper, we consider the dual approach, where the volume of $H$ is maximized instead; this is referred to as maximum-volume NMF (MaxVol NMF). MaxVol NMF is identifiable under the same conditions as MinVol NMF in the noiseless case, but it behaves rather differently in the presence of noise. In practice, MaxVol NMF is much more effective to extract a sparse decomposition and does not generate rank-deficient solutions. In fact, we prove that the solutions of MaxVol NMF with the largest volume correspond to clustering the columns of $X$ in disjoint clusters, while the solutions of MinVol NMF with smallest volume are rank deficient. We propose two
algorithms to solve MaxVol NMF. We also present a normalized variant of MaxVol NMF that exhibits better performance than MinVol NMF and MaxVol NMF, and can be interpreted as a continuum between standard NMF and orthogonal NMF. We illustrate our results in the context of hyperspectral unmixing. The code is available from https://gitlab.com/vuthanho/maxvolmf.jl.
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Audio and Speech Processing · Cross-listed from cs.SD
Speaker-Aware Simulation Improves Conversational Speech Recognition
Máté Gedeon and Péter Mihajlik
Automatic
speech recognition (ASR) for conversational
speech remains challenging due to the limited availability of large-scale, well-annotated multi-speaker dialogue data and the complex temporal dynamics of natural interactions. Speaker-aware simulated conversations (SASC) offer an effective data augmentation strategy by transforming single-speaker recordings into realistic multi-speaker dialogues. However, prior work has primarily focused on English data, leaving questions about the applicability to lower-resource
languages. In this paper, we adapt and implement the SASC framework for Hungarian conversational ASR. We further propose C-SASC, an extended variant that incorporates pause modeling conditioned on utterance duration, enabling a more faithful representation of local temporal dependencies observed in human conversation while retaining the simplicity and efficiency of the original approach. We generate synthetic Hungarian dialogues from the BEA-Large corpus and combine them with real conversational data for ASR training. Both SASC and C-SASC are evaluated extensively under a wide range of simulation configurations, using conversational statistics derived from CallHome, BEA-Dialogue, and GRASS corpora. Experimental results show that speaker-aware conversational simulation consistently improves recognition performance over naive concatenation-based augmentation. While the additional duration conditioning in C-SASC yields modest but systematic gains–most notably in character-level error rates–its effectiveness depends on the match between source conversational statistics and the target domain. Overall, our findings confirm the robustness of speaker-aware conversational simulation for Hungarian ASR and highlight the benefits and limitations of increasingly detailed temporal modeling in synthetic dialogue generation.
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Systems and Control
Control Lyapunov Functions for Optimality in Sontag-Type Control
Joscha F. Bongard and Boris Lohmann
Given a Control Lyapunov Function (CLF), Sontag's famous Formula provides a nonlinear state-feedback guaranteeing asymptotic stability of the setpoint. At the same time, a cost function that depends on the CLF is minimized. While there exist methods to construct CLFs for certain classes of systems, the impact on the resulting performance is unclear. This article aims to make two contributions to this problem: (1) We show that using the value function of an LQR design as CLF, the resulting Sontag-type controller minimizes a classical quadratic cost around the setpoint and a CLF-dependent cost within the domain where the CLF condition holds. We also show that the closed-loop system is stable within a local region at least as large as that generated by the LQR. (2) We show a related CLF design for feedback-linearizable systems resulting in a global CLF in a straight-forward manner; The Sontag design then guarantees global asymptotic stability while minimizing a quadratic cost at the setpoint and a CLF-dependent cost in the whole state-space. Both designs are constructive and easily applicable to nonlinear multi-input systems under mild assumptions.
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Systems and Control
Dynamic Constraint Tightening for Nonlinear MPC for Autonomous Racing via Contraction Analysis
Joscha F. Bongard, Valentin L. Krieger and Boris Lohmann
This work develops a robust nonlinear Model Predictive Control (MPC) framework for path tracking in autonomous vehicles operating at the limits of handling utilizing a Control Contraction Metric (CCM) derived from a perturbed dynamic single track model. We first present a nonlinear MPC scheme for autonomous vehicles. Building on this nominal scheme, we assume limited uncertainty in tire parameters as well as bounded force disturbances in both lateral and longitudinal directions. By simplifying the perturbed model, we optimize a CCM for the uncertain model, which is validated through simulations at the dynamic limits of vehicle performance. This CCM is subsequently employed to parameterize a homothetic tube used for constraint tightening within the MPC formulation. The resulting robust nonlinear MPC is computationally more efficient than competing methods, as it introduces only a single additional state variable into the prediction model compared to the nominal scheme. Simulation results demonstrate that the homothetic tube expands most significantly in regions where the nominal scheme would otherwise violate constraints, illustrating its ability to capture all uncertain trajectories while avoiding unnecessary conservatism.
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Signal Processing
Scalable Cross-Attention Transformer for Cooperative Multi-AP OFDM Uplink Reception
Xavier Tardy, Grégoire Lefebvre, Apostolos Kountouris et al. (+2 more)
We propose a cross-
attention Transformer for joint decoding of uplink OFDM signals received by multiple coordinated access points. A shared per-receiver encoder learns the time-frequency structure of each grid, and a
token-wise cross-
attention module fuses the receivers to produce soft log-likelihood ratios for a standard channel decoder without explicit channel estimates. Trained with a bit-metric objective, the model adapts its fusion to per-receiver reliability and remains robust under degraded links, strong frequency selectivity, and sparse pilots. Over realistic Wi-Fi channels, it outperforms classical pipelines and strong neural baselines, often matching or surpassing a local perfect-CSI reference while remaining compact and computationally efficient on commodity hardware, making it suitable for next-generation coordinated Wi-Fi receivers.
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All authors Xavier Tardy, Grégoire Lefebvre, Apostolos Kountouris, Haïfa Fares, Amor Nafkha
Signal Processing · Cross-listed from cs.LG
Benchmarking and Enhancing PPG-Based Cuffless Blood Pressure Estimation Methods
Neville Mathew, Yidan Shen, Renjie Hu et al. (+2 more)
Cuffless blood pressure screening based on easily acquired photoplethysmography (PPG) signals offers a practical pathway toward scalable cardiovascular health assessment. Despite rapid progress, existing PPG-based blood pressure estimation models have not consistently achieved the established clinical numerical limits such as AAMI/ISO 81060-2, and prior evaluations often lack the rigorous experimental controls necessary for valid clinical assessment. Moreover, the publicly available
datasets commonly used are heterogeneous and lack physiologically controlled conditions for fair benchmarking. To enable fair benchmarking under physiologically controlled conditions, we created a standardized benchmarking subset NBPDB comprising 101,453 high-quality PPG segments from 1,103 healthy adults, derived from MIMIC-III and VitalDB. Using this
dataset, we systematically benchmarked several state-of-the-art PPG-based models. The results showed that none of the evaluated models met the AAMI/ISO 81060-2 accuracy requirements (mean error $<$ 5 mmHg and standard deviation $<$ 8 mmHg). To improve model accuracy, we modified these models and added patient demographic data such as age, sex, and body mass index as additional inputs. Our modifications consistently improved performance across all models. In particular, the MInception model reduced error by 23% after adding the demographic data and yielded mean absolute errors of 4.75 mmHg (SBP) and 2.90 mmHg (DBP), achieves accuracy comparable to the numerical limits defined by AAMI/ISO accuracy standards. Our results show that existing PPG-based BP estimation models lack clinical practicality under standardized conditions, while incorporating demographic information markedly improves their accuracy and physiological validity.
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All authors Neville Mathew, Yidan Shen, Renjie Hu, Maham Rahimi, George Zouridakis
Systems and Control · Cross-listed from math.DS
On Data-Driven Unbiased Predictors using the Koopman Operator
Roland Schurig, Pieter van Goor, Karl Worthmann et al. (+1 more)
The Koopman operator and its data-driven approximations, such as extended dynamic mode decomposition (EDMD), are widely used for analysing, modelling, and controlling nonlinear dynamical systems. However, when the true Koopman eigenfunctions cannot be identified from finite data, multi-step predictions may suffer from structural inaccuracies and systematic bias. To address this issue, we analyse the first and second moments of the multi-step prediction residual. By decomposing the residual into contributions from the one-step approximation error and the propagation of accumulated inaccuracies, we derive a closed-form expression characterising these effects. This analysis enables the development of a novel and computationally efficient
algorithm that enforces unbiasedness and reduces variance in the resulting predictor. The proposed method is validated in numerical simulations, showing improved uncertainty properties compared to standard EDMD. These results lay the foundation for uncertainty-aware and unbiased Koopman-based prediction frameworks that can be extended to controlled and
stochastic systems.
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All authors Roland Schurig, Pieter van Goor, Karl Worthmann, Rolf Findeisen
Image and Video Processing · Cross-listed from cs.CV
SAR-RAG: ATR Visual Question Answering by Semantic Search, Retrieval, and MLLM Generation
David F. Ramirez, Tim Overman, Kristen Jaskie et al. (+2 more)
We present a visual-context image-
retrieval-augmented generation (ImageRAG)- assisted AI
agent for automatic target recognition (ATR) of synthetic aperture radar (SAR) imagery. SAR is a remote sensing method used in defense and security applications to detect and monitor the positions of military vehicles, which may appear indistinguishable in images. Researchers have extensively studied SAR ATR to improve the differentiation and identification of vehicle types, characteristics, and measurements. Test examples can be compared with known vehicle target types to improve recognition tasks. New methods enhance the capabilities of neural networks,
transformer attention, and
multimodal large
language models. An agentic AI method may be developed to utilize a defined set of tools, such as searching through a library of similar examples. Our proposed method, SAR
Retrieval-Augmented Generation (SAR-RAG), combines a
multimodal large
language model (MLLM) with a vector database of semantic
embeddings to support contextual search for image exemplars with known qualities. By recovering past image examples of known true target types, our SAR-RAG system can compare similar vehicle categories, thereby improving ATR prediction accuracy. We evaluate this through search and
retrieval metrics, categorical classification accuracy, and numeric regression of vehicle dimensions. These metrics all show improvements when SAR-RAG is added to an MLLM baseline method as an attached ATR
memory bank.
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All authors David F. Ramirez, Tim Overman, Kristen Jaskie, Joe Marvin, Andreas Spanias
Signal Processing
Resilient Channel Charting Under Varying Radio Link Availability
Jonas Pirkl, Jonathan Ott, Maximilian Stahlke et al. (+3 more)
Channel charting (CC) has become a key technology for RF-based localization, enabling unsupervised
radio fingerprinting, even in non line of sight scenarios, with a minimum of reference position labels. However, most CC models assume fixed-size inputs, such as a constant number of
antennas or channel measurements. In practical systems,
antennas may fail, signals may be blocked, or
antenna sets may change during handovers, making fixed-input architectures fragile. Existing
radio-fingerprinting approaches address this by training separate models for each
antenna configuration, but the resulting training effort scales prohibitively with the array size. We propose Adaptive Positioning (AdaPos), a CC architecture that natively handles variable numbers of channel measurements. AdaPos combines convolutional feature extraction with a
transformer-based encoder using learnable
antenna identifiers and self-
attention to fuse arbitrary subsets of CSI inputs. Experiments on two public real-world
datasets (SISO and
MIMO) show that AdaPos maintains state-of-the-art accuracy under missing-
antenna conditions and replaces roughly 57 configuration-specific models with a single unified model. With AdaPos and our novel training strategies, we provide resilience to both individual
antenna failures and full-array outages.
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All authors Jonas Pirkl, Jonathan Ott, Maximilian Stahlke, George Yammine, Tobias Feigl, Christopher Mutschler
Signal Processing
Knowledge Distillation for mmWave Beam Prediction Using Sub-6 GHz Channels
Sina Tavakolian, Nhan Thanh Nguyen, Ahmed Alkhateeb et al. (+1 more)
Beamforming in millimeter-wave (mmWave) high-mobility environments typically incurs substantial training overhead. While prior studies suggest that sub-6 GHz channels can be exploited to predict optimal mmWave beams, existing methods depend on large deep learning (DL) models with prohibitive computational and
memory requirements. In this paper, we propose a computationally efficient framework for sub-6 GHz channel-mmWave beam mapping based on the knowledge
distillation (KD) technique. We develop two compact student DL architectures based on individual and relational
distillation strategies, which retain only a few hidden layers yet closely mimic the performance of large teacher DL models. Extensive simulations demonstrate that the proposed student models achieve the teacher's beam prediction accuracy and spectral efficiency while reducing trainable parameters and computational complexity by 99%.
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All authors Sina Tavakolian, Nhan Thanh Nguyen, Ahmed Alkhateeb, Markku Juntti
Signal Processing
HFMCA: Orthonormal Feature Learning for EEG-based Brain Decoding
Yinghao Wang, Lintao Xu, Shujian Yu et al. (+2 more)
Electroencephalography (
EEG) analysis is critical for
brain-computer interfaces and neuroscience, but the intrinsic noise and high dimensionality of
EEG signals hinder effective feature learning. We propose a self-supervised framework based on the Hierarchical Functional Maximal Correlation
Algorithm (HFMCA), which learns orthonormal
EEG representations by enforcing feature decorrelation and reducing redundancy. This design enables robust capture of essential
brain dynamics for various
EEG recognition tasks. We validate HFMCA on two
benchmark datasets, SEED and BCIC-2A, where pretraining with HFMCA consistently outperforms competitive self-supervised baselines, achieving notable gains in classification accuracy. Across diverse
EEG tasks, our method demonstrates superior cross-subject generalization under leave-one-subject-out validation, advancing state-of-the-art by 2.71% on SEED
emotion recognition and 2.57% on BCIC-2A motor imagery classification.
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All authors Yinghao Wang, Lintao Xu, Shujian Yu, Enzo Tartaglione, Van-Tam Nguyen
Systems and Control
Output-Positive Adaptive Control of Parabolic PDE-ODE Cascades
Yun Jiang and Ji Wang
In this paper, we propose a safe adaptive boundary control strategy for a class of
parabolic partial differential equation-ordinary differential equation (PDE-ODE) cascaded systems with parametric uncertainties in both the PDE and ODE subsystems. The proposed design is built upon an adaptive Control Barrier Function (aCBF) framework that incorporates high-relative-degree CBFs together with a batch least-squares identification (BaLSI)-based adaptive control that guarantees exact parameter identification in finite time. The proposed controller ensures the positivity, i.e., the safety, of the plant output state that is the furthest state from the control input, as well as the exponential regulation of the overall plant state to zero. Numerical simulations are provided to demonstrate the effectiveness of the proposed approach.
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Signal Processing
Learning to Separate RF Signals Under Uncertainty: Detect-Then-Separate vs. Unified Joint Models
Ariel Rodrigez, Alejandro Lancho and Amir Weiss
The increasingly crowded
radio frequency (RF) spectrum forces communication signals to coexist, creating heterogeneous interferers whose structure often departs from Gaussian models. Recovering the interference-contaminated signal of interest in such settings is a central challenge, especially in single-channel RF processing. Existing data-driven methods often assume that the interference type is known, yielding ensembles of specialized models that scale poorly with the number of interferers. We show that detect-then-separate (DTS) strategies admit an analytical justification: within a Gaussian mixture framework, a plug-in maximum a posteriori detector followed by type-conditioned optimal estimation achieves asymptotic minimum mean-square error optimality under a mild temporal-diversity condition. This makes DTS a principled
benchmark, but its reliance on multiple type-specific models limits scalability. Motivated by this, we propose a unified joint model (UJM), in which a single deep neural architecture learns to jointly detect and separate when applied directly to the received signal. Using tailored UNet architectures for baseband (complex-valued) RF signals, we compare DTS and UJM on synthetic and recorded interference types, showing that a capacity-matched UJM can match oracle-aided DTS performance across diverse signal-to-interference-and-noise ratios, interference types, and constellation orders, including mismatched training and testing type-uncertainty proportions. These findings highlight UJM as a scalable and practical alternative to DTS, while opening new directions for unified separation under broader regimes.
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Signal Processing
Total Variation Sparse Bayesian Learning for Block Sparsity via Majorization-Minimization
Yanbin He and Geethu Joseph
Block sparsity is a widely exploited structure in sparse recovery, offering significant gains when signal blocks are known. Yet, practical signals often exhibit unknown block boundaries and isolated non-zero entries, which challenge traditional approaches. A promising method to handle such complex sparsity patterns is the difference-of-logs total variation (DoL-TV) regularized sparse
Bayesian learning (SBL). However, due to the complex form of DoL-TV term, the resulting optimization problem is hard to solve. This paper develops a new optimization framework for the DoL-TV SBL cost function. By introducing an exponential reparameterization of the SBL hyperparameters, we reveal a novel structure that admits a majorization-minimization formulation and naturally extends to unknown noise variance estimation. Sparse recovery results on both synthetic data and extended source direction-of-arrival estimation demonstrate improved accuracy and runtime performance compared to
benchmark methods.
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Systems and Control · Cross-listed from cs.LG
Resilient Load Forecasting under Climate Change: Adaptive Conditional Neural Processes for Few-Shot Extreme Load Forecasting
Chenxi Hu, Yue Ma, Yifan Wu et al. (+1 more)
Extreme weather can substantially change electricity consumption behavior, causing load curves to exhibit sharp spikes and pronounced
volatility. If forecasts are inaccurate during those periods, power systems are more likely to face supply shortfalls or localized overloads, forcing emergency actions such as load shedding and increasing the risk of service disruptions and public-safety impacts. This problem is inherently difficult because extreme events can trigger abrupt regime shifts in load patterns, while relevant extreme samples are rare and irregular, making reliable learning and calibration challenging. We propose AdaCNP, a probabilistic
forecasting model for data-scarce condition. AdaCNP learns similarity in a shared
embedding space. For each target data, it evaluates how relevant each historical context segment is to the current condition and reweights the context information accordingly. This design highlights the most informative historical evidence even when extreme samples are rare. It enables few-shot adaptation to previously unseen extreme patterns. AdaCNP also produces predictive distributions for risk-aware decision-making without expensive fine-tuning on the target domain. We evaluate AdaCNP on real-world power-system load data and compare it against a range of representative baselines. The results show that AdaCNP is more robust during extreme periods, reducing the mean squared error by 22% relative to the strongest baseline while achieving the lowest negative log-likelihood, indicating more reliable probabilistic outputs. These findings suggest that AdaCNP can effectively mitigate the combined impact of abrupt distribution shifts and scarce extreme samples, providing a more trustworthy
forecasting for resilient power system operation under extreme events.
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All authors Chenxi Hu, Yue Ma, Yifan Wu, Yunhe Hou
Systems and Control
Reinforcement Learning-based Home Energy Management with Heterogeneous Batteries and Stochastic EV Behaviour
Meng Yuan, Ye Wang, Xinghuo Yu et al. (+2 more)
The widespread adoption of photovoltaic (PV), electric vehicles (EVs), and stationary energy storage systems (ESS) in households increases system complexity while simultaneously offering new opportunities for energy regulation. However, effectively coordinating these resources under uncertainties remains challenging. This paper proposes a novel home energy management framework based on deep reinforcement learning (DRL) that can jointly minimise energy expenditure and battery degradation while guaranteeing occupant comfort and EV charging requirements. Distinct from existing studies, we explicitly account for the heterogeneous degradation characteristics of stationary and EV batteries in the optimisation, alongside
stochastic user behaviour regarding arrival time, departure time, and driving distance. The energy scheduling problem is formulated as a constrained Markov decision process (CMDP) and solved using a Lagrangian soft actor-critic (SAC)
algorithm. This approach enables the
agent to learn optimal control policies that enforce physical constraints, including indoor temperature bounds and target EV state of charge upon departure, despite
stochastic uncertainties. Numerical simulations over a one-year horizon demonstrate the effectiveness of the proposed framework in satisfying physical constraints while eliminating thermal oscillations and achieving significant economic benefits. Specifically, the method reduces the cumulative operating cost substantially compared to two standard rule-based baselines while simultaneously decreasing battery degradation costs by 8.44%.
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All authors Meng Yuan, Ye Wang, Xinghuo Yu, Torsten Wik, Changfu Zou
Systems and Control
Peak Bounds for the Estimation Error under Sensor Attacks
Axel Stafström, Daniel Arnström, Adam Miksits et al. (+1 more)
This paper investigates bounds on the estimation error of a linear system affected by norm-bounded disturbances and full sensor attacks. The system is equipped with a detector that evaluates the norm of the innovation signal to detect faults, and the attacker wants to avoid detection. We utilize induced $L_\infty$ system norms, also called peak-to-peak norms, to compare the estimation error bounds under nominal operations and under attack. This leads to a sufficient condition for when the bound on the estimation error is smaller during an attack than during nominal operation. This condition is independent of the attack strategy and depends only on the attacker's desire to remain undetected and (indirectly) the observer gain. Therefore, we investigate both an observer design method, that seeks to reduce the error bound under attack while keeping the nominal error bound low, and detector threshold tuning. As a numerical illustration, we show how a sensor attack can deactivate a robust safety filter based on control barrier functions if the attacked error bound is larger than the nominal one. We also statistically evaluate our observer design method and the effect of the detector threshold.
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All authors Axel Stafström, Daniel Arnström, Adam Miksits, David Umsonst
Signal Processing
An Information-Theoretic Detector for Multiple Scatterers in SAR Tomography
Pia Addabbo, Diego Reale, Antonio Pauciullo et al. (+2 more)
Persistent scatterer interferometry and Synthetic Aperture Radar (SAR)
Tomography are powerful tools for the detection and time monitoring of persistent scatterers. They have been proven to be effective in urban scenarios, especially for buildings and infrastructures 3-D reconstruction and monitoring of deformation. In urban areas, occurrence of layover leads to the presence of multiple contributions within the same image pixel from scatterers located at different heights. In the context of SAR
Tomography, this problem can be addressed by considering a multiple hypothesis test to detect the presence of feasible multiple scatterers [1][2]. In the present paper, we consider this problem in the framework of the information theory and exploit the theoretical tool, developed in [3], to design a one-stage adaptive architecture for multiple hypothesis testing problems in the context of SAR
Tomography. Moreover, we resort to the compressive sensing approach for the estimation of the unknown parameters under each hypothesis. This architecture has been verified on both simulated as well as real data also in comparison with suitable counterparts.
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All authors Pia Addabbo, Diego Reale, Antonio Pauciullo, Gianfranco Fornaro, Danilo Orlando
Signal Processing
Rigid Body Localization via Gaussian Belief Propagation with Quadratic Angle Approximation
Niclas Führling, Hyeon Seok Rou, Giuseppe Thadeu Freitas de Abreu et al. (+2 more)
Gaussian belief propagation (GaBP) is a technique that relies on linearized error and input output models to yield low-complexity solutions to complex estimation problems, which has been recently shown to be effective in the design of range-based GaBP schemes for stationary and moving rigid body localization (RBL) in three-dimensional (3D) space, as long as the relative rotation between the prior position and the target rigid body is sufficiently small. In this article we present a novel range-based RBL scheme via GaBP that relaxes the latter limitation significantly. To this end, the proposed method incorporates a quadratic angle approximation to linearize the relative orientation between the prior and the target rigid body, enabling high precision estimates of corresponding rotation angles even for large deviations. Leveraging the resulting linearized model, we derive the corresponding message-passing (MP) rules to obtain estimates of the translation vector and rotation
matrix of the target rigid body, relative to a prior reference frame. Numerical results corroborate the good performance of the proposed angle approximation itself, as well as the consequent RBL performance in terms of root mean square errors (RMSEs) in comparison to the state-of-the-art (SotA), while maintaining a low computational complexity.
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All authors Niclas Führling, Hyeon Seok Rou, Giuseppe Thadeu Freitas de Abreu, David González G., Osvaldo Gonsa
Signal Processing
An Enhanced Polar-Domain Dictionary Design for Elevated BSs in Near-Field U-MIMO
Luca Antonelli, Antonio Alberto D'Amico and Luca Sanguinetti
Near-field U-
MIMO communications require carefully optimized sampling grids in both angular and distance domains. However, most existing grid design methods neglect the influence of base station height, assuming instead that the base station is positioned at ground level - a simplification that rarely reflects real-world deployments. To overcome this limitation, we propose a generalized grid design framework that accommodates arbitrary base station locations. Unlike conventional correlation-based approaches, our method optimizes the grid based on the minimization of the optimal normalized mean squared error, leading to more accurate channel representation. We evaluate the performance of a hybrid U-
MIMO system operating at sub-THz frequencies, considering the P-SOMP
algorithm for channel estimation. Analytical and numerical results show that the proposed design enhances both channel estimation accuracy and spectral efficiency compared to existing alternatives.
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Signal Processing
A Low-Complexity Joint Fractional Delay and Doppler Frequency Estimator for AFDM-Enabled Vehicular LEO-ICAN Systems
Zhenyu Chen, Ke Xiao, Xiaomei Tang et al. (+3 more)
Low-Earth-orbit (LEO) satellites and vehicle-to-everything (V2X) networks are driving integrated communication and
navigation (ICAN) toward next-generation intelligent transportation. Affine frequency division multiplexing (AFDM) is a promising waveform for high-mobility LEO scenarios owing to its Doppler robustness, simple modulation, and low pilot overhead. However, applying existing high-accuracy AFDM fractional delay-Doppler
estimators to LEO-ICAN entails substantial search or inference complexity, while the spectrum-wrapping-induced envelope structure in line-of-sight (LOS)-dominated channels remains underexploited. This paper analyzes and exploits the spectrum-wrapping-induced envelope structure of the fractional AFDM response, and proposes a low-complexity joint
estimator that combines minimum-
entropy fractional Doppler estimation with closed-form fractional delay estimation. Simulation results show that the proposed
estimator approaches the root Cramér–Rao lower bound (RCRLB) and achieves root-mean-square error (RMSE) performance comparable to that of matched filtering (MF), matched filtering with generalized Fibonacci search (MF-GFS), and off-grid sparse
Bayesian learning (OG-SBL), while requiring substantially lower computational complexity and runtime. This favorable accuracy-complexity profile highlights the potential of the proposed
estimator for real-time ICAN processing in high-mobility LEO-assisted vehicular networks.
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All authors Zhenyu Chen, Ke Xiao, Xiaomei Tang, Jing Lei, Muzi Yuan, Guangfu Sun